A BLOG ABOUT SOUTHWESTERN WEATHER,WEATHER FORECASTING & OBSERVING, AND OTHER RELATED TOPICS

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Saturday, December 16, 2017

Tomorrow's Weather Event

Yesterday was cold here at house with a low of 36 F sometime before the east winds started, which was before sunrise. Winds were surprisingly strong here in this part of town with some blowing dust and gusts 35 to 40 mph between about 8:00 and 11:00 am MST.Rainfall here has been almost non-existent since August 13th when there was 1.16" - since then the two heaviest rain days were August 26th with 0.14" and September 7th with 0.11". Even though tomorrow's system will be short on moisture, it will still bring a chance for the heaviest precipitation event since mid-August, so that makes it a pretty big deal.

The 06 UTC plumes of forecast PW (above) from the GEFS for TUS indicate a significant increase from this morning to maximum amounts over 0.50 inches tomorrow afternoon. This occurs because the current forecasts dig the closed, 500 mb low a bit west of northern Baja, allowing the system to pick up some moisture from the south before it swings eastward. The plumes for rainfall at TUS (from the same run of the GEFS - below) show that all of the members forecast measurable rain at the airport, but with amounts ranging from 0.02" to about 0.40". The amounts here will depend very much on the exact track that the 500 mb low takes.

The 06 UTC WRF-GFS from Atmo forecasts the most significant radar echoes over Pima County to occur during early afternoon tomorrow (above forecast of composite radar echoes valid at 1:00 pm).That model run currently forecasts the 500 mb low to pass nearly overhead (below valid at 7:00 pm tomorrow) with temperatures colder than -20 C. The model forecasts of QPF from this run are only a tenth of an inch at TUS, but are over an inch at Nogales and Sierra Vista. Will be very important to see the details of exactly where the system moves tomorrow.